The present invention relates to a method for the preparation of methyl hydrogensilanes or, more particularly, for the preparation of dimethylsilane and 1,1,2,2-tetramethyl disilane by the pyrolysis of a methyl polysilane compound.
Methyl hydrogenchlorosilane compounds, e.g. dimethyl monochlorosilane, are useful in the industry of silicones as an intermediate for the synthetic preparation of various organosilicon compounds having reactive or functional groups by virtue of the reactivity of the hydrogen atoms directly bonded to the silicon atom and the hydrolyzability of the chlorine atom in the molecule into a silanolic hydroxy group susceptible to dehydration condensation to give a siloxane linkage. Notwithstanding the large demand for such methyl hydrogenchlorosilanes for the applications as mentioned above, the supply of the compounds in the silicone industry is limited. That is, methyl hydrogenchlorosilanes are obtained industrially only as a byproduct is a relatively small amount in the so-called direct method for the synthesis of methyl chlorosilanes by the reaction of metallic silicon and methyl chloride. Various attempts have been made, of course, to develop an efficient method for increasing the yield of the methyl hydrogenchlorosilanes in the above mentioned direct method or for establishing another efficient synthetic route for the preparation thereof though without noticeable success to give only a few percent yield of, for example, methyl dichlorosilane CH.sub.3 SiHCl.sub.2. In particular, it has been eagerly desired to establish an industrially feasible method for the preparation of dimethyl monochlorosilane (CH.sub.3).sub.2 HSiCl since the yield of this particular methyl hydrogenchlorosilane as a byproduct in the direct method is very small even in comparison with the yield of the above mentioned methyl dichlorosilane.
It is one of possible ways to obtain the above mentioned dimethyl monochlorosilane from dimethylsilane (CH.sub.3).sub.2 SiH.sub.2 or 1,1,2,2-tetramethyl disilane (CH.sub.3).sub.2 HSi--SiH(CH.sub.3).sub.2 utilizing the reactivity of the silicon-bonded hydrogen atoms or the susceptibility of the Si--Si linkage to scission. Unfortunately, the supply of these methyl hydrogensilanes is also limited since no industrially practicable method is known for the preparation thereof.